Conventional photovoltaic (PV) systems generate electricity by direct exposure to the sun, i.e., they are designed for substantially 1-sun operation. In contrast concentrator PV systems rely on optical devices (e.g., mirrors) to concentrate more than one sun worth of solar radiation on a solar collector.
Concentrator PV systems scale in size differently than conventional flat-plate photovoltaic systems, which are made for substantially 1-sun operation. Conventional PV is scaled by adding more panels (i.e., surface area) to generate different amounts of electricity. However, increasing the power output of a particular system requires additional PV cells, and large areas of semi-conductor PV cells are expensive. Concentrator PV uses optical devices to increase the solar energy landing on the expensive PV cells, reducing the cost of the PV system. Concentrator systems have attempted to track the sun's relative motion in the sky to allow for efficient optical concentration of solar energy during the course of a day. It is important to note that the angle of the sun relative to a particular geographic location also changes throughout the year, i.e., through the course of the seasons.
Further, the scaling of convex lens optical systems for concentrator systems to regulate the amount of power output is limited by the mass of material needed to form a larger concentrator. A paraboloid is a specific shape which can reflect parallel rays of light to a point. It can be scaled to any size but the shape always stays the same. A common parameter for scaling the paraboloid is the focal length, f. For a given focal length, the active area of a paraboloidal concentrator is increased by increasing the diameter, d, of the physical reflective part of the concentrator.
In principle, devices with the highest optical quality are simply the largest possible paraboloidal reflectors symmetric about the optical axis gathering light incident along that axis. A paraboloid, however, tends to use a large amount of materials, is difficult to construct accurately while maintaining shape under varying gravity and wind loads, and requires a substantial structure for tracking the sun in the sky.
Thus, a need exists for solar concentrator systems which are energy efficient, cost efficient and which track the sun's motion through the sky.